At the local post office, customers join a single line where they are routed to the first available

of $4$ postal service workers for help with their transaction, e$.$g$.$ purchasing postage, weighing

the package, answering questions. The time it takes the postal service worker to complete the

transaction is $5\mathrm{.}1$ minutes on average with a standard deviation of $5\mathrm{.}8$ minutes. During the

busy holiday rush, customers arrive at the post office every $2$ minutes on average with a

standard deviation of $1\mathrm{.}2$ minutes.

Calculate the average total time a customer spends at the post office including time spent

waiting and in service.

Carry intermediate calculations to at least $3$ decimal places.

Enter your final answer rounded to one decimal place.